extends layout
append styles
    style.
        body { background-color:lightgreen; }
        /* @media mediatype and|not|only (media feature) */
        @media screen and (max-width: 900px) {  /* 如果文档宽度小于 300 像素则修改背景演示 */
            body { background-color:lightblue; }
        }
block content
